1. Field of the Invention
The present invention related to an image forming apparatus and a process cartridge in which it is possible to effectively eliminate electric charge on a transfer medium onto which a toner image formed on an electrostatic latent image carrier can be transferred.
2. Description of the Related Art
A conventional laser beam printer includes a photosensitive drum. An electrostatic latent image can be formed on the cylindrical surface of the photosensitive drum with a laser beam. A visible image can be elicited with toner supplied to the latent image. The visible image on the photosensitive drum can be transferred onto one side of a sheet of paper by the attractive force of the electric charge supplied to the other side of the sheet. After the visible image is transferred onto the sheet, the electric charge accumulated on the sheet may cause a paper jam and prevent the sheet from being fed smoothly.
In order to avoid paper jams and smooth the paper feeding, the conventional printer includes a static eliminator for moderately eliminating the electric charge accumulated on a sheet of paper. Such a static eliminator of the ordinary type needs to be grounded, and consequently its design and manufacturing process are complicated.
In recent years, fibrous electric conductors may be used as static eliminators, which do not need to be grounded. A fibrous electric conductor is very suitable as a static eliminator because it can effectively eliminate electric charge by repeating a minute amount of discharge from the ends of its intertwined conducting fibers (self-discharge effect).
However, static electricity fluffs the fibrous conductor. When the fluff touches that side of a sheet of paper where no image is formed, an excessive amount of electric charge accumulated on the sheet may be eliminated. The excessive elimination weakens the attractive force between the sheet and the toner transferred onto it. This disturbs or distorts the toner image formed on the sheet. If the fibrous conductor and the sheet are spaced from each other so that the fluff does not touch the sheet, it is not possible to eliminate a sufficient amount of electric charge accumulated on the sheet.
It is an object of the present invention to provide an image forming apparatus for stably feeding paper and for forming a high-quality image on the paper by effectively eliminating the electric charge accumulated on the paper after toner is transferred onto the paper. It is another object to provide a process cartridge for use in such an image forming apparatus.
In accordance with a first aspect of the present invention, an image forming apparatus is provided, which comprises a feed path, an electrostatic latent image carrier, a transferring unit and a static eliminator. A transfer medium can pass along the feed path. The latent image carrier can be supplied with a developer. The transferring unit transfers, onto one side of the transfer medium passing along the feed path, the developer supplied to the latent image carrier. The static eliminator is provided downstream from the transferring unit in the feed path, and eliminates electric charge accumulated on the passing medium. The static eliminator includes a fibrous electric conductor and a non-fibrous electric conductor, which are connected electrically with each other. The non-fibrous conductor is positioned between the fibrous conductor and the other side of the passing medium.
The non-fibrous conductor between the fibrous conductor and the transfer medium passing along the feed path prevents the surfaces of the fibrous conductor from fluffing, and enables the fibrous conductor to self-discharge. This makes it possible to simplify the design and production processes, smooth the paper feeding, and prevent the image quality from worsening.
The fibrous conductor may be an electrically conducting nonwoven fabric, which includes fine fibers for better self-discharge effect.
The fibrous conductor may include electrically conducting fibers having a diameter of 4.5 or less microns for full self-discharge effect. In order to further enhance the self-discharge effect, electronically conjugate polymers may be reactively formed on the conducting fibers.
The non-fibrous conductor may be a sheet lying along the fibrous conductor. Without spoiling the self-discharge effect of the fibrous conductor, this sheet prevents the fibrous conductor from fluffing, and conducts electric charge effectively to it.
The non-fibrous conductor may be a resin sheet with an aluminum film formed on it for higher conductivity, which results in more effective static elimination from the transfer medium.
The non-fibrous conductor may be positioned out of contact with the transfer medium passing along the feed path. This prevents excessive elimination of electric charge, which would occur if the transfer medium touched the static eliminator. The prevention results in stable static elimination.
In accordance with a second aspect of the present invention, a process cartridge is provided, which can be fitted to and removed from an image forming apparatus. The apparatus has a feed path formed therein along which a transfer medium can pass. The process cartridge includes a transferring unit for transferring developer onto one side of the passing transfer medium. The process cartridge includes an electrostatic latent image carrier contacting with the transferring unit. The process cartridge also includes a static eliminator for eliminating electric charge accumulated on the transfer medium. The static eliminator is provided downstream from the transferring unit in the feed path. The static eliminator includes a fibrous electric conductor and a non-fibrous electric conductor that are connected electrically with each other. The non-fibrous conductor is positioned between the fibrous conductor and the other side of the passing transfer medium.